Kidney stones in adults: Kidney stones during pregnancy

INTRODUCTION — Kidney stone disease (nephrolithiasis) is a common problem in primary care practice. Patients may present with the classic symptoms of renal colic and hematuria. Others may be asymptomatic or have atypical symptoms such as vague abdominal pain, acute abdominal or flank pain, nausea, urinary urgency or frequency, or difficulty urinating.

This topic will review the diagnosis and management of kidney stones during pregnancy. Other aspects of kidney stones in adults are discussed separately:

●(See "Kidney stones in adults: Epidemiology and risk factors".)

●(See "Kidney stones in adults: Diagnosis and acute management of suspected nephrolithiasis".)

●(See "Kidney stones in adults: Evaluation of the patient with established stone disease".)

●(See "Kidney stones in adults: Prevention of recurrent kidney stones".)

●(See "Kidney stones in adults: Surgical management of kidney and ureteral stones".)

EPIDEMIOLOGY — The development of a symptomatic stone during pregnancy is a rare event, occurring in approximately 1 in every 500 to 3000 pregnancies [1-3]. While earlier studies reported similar rates of kidney stones between pregnant and nonpregnant females of childbearing age [4-6], a case-control study that compared 945 female first-time symptomatic kidney stone formers aged 15 to 45 years with 1890 aged-matched female controls reported a higher risk during pregnancy [7]. There was no difference in risk in the first trimester, but the risk was twofold higher during the second trimester and 2.7-fold higher during the third trimester; the risk peaked at zero to three months after delivery and returned to baseline one year after delivery. However, this study was unable to determine if the stone formed during pregnancy or if an existing stone was just more likely to become symptomatic during that time.

A study of over 1.3 million pregnancies in Canada found an increased risk of adverse birth outcomes in pregnancies with kidney stones [3].

RISK FACTORS IN PREGNANCY — Most pregnant patients who develop kidney stones do not have a prior history of stone disease [2]. However, it is not clear whether such patients have a preexisting stone or an underlying tendency to stone formation or whether factors related to pregnancy are responsible.

Normal pregnancy is associated with an increase in urine calcium excretion (243 versus 194 mg/day in one series), smaller increases in urine citrate and magnesium excretion (which protect against stone formation), and a rise in urine pH but not urine volume [8]. The urine supersaturation for calcium oxalate is similar to that in nonpregnant females with calcium stones.

Additional factors that contribute to stone formation during pregnancy may include urinary stasis, secondary to increased progesterone levels, and diminished fluid intake during late pregnancy, as a result of decreasing bladder capacity from the gravid uterus.

A more detailed discussion of risk factors for kidney stone disease among adults is presented separately. (See "Kidney stones in adults: Epidemiology and risk factors".)

CLINICAL PRESENTATION — Affected patients usually present in the second or third trimester (approximately 20 percent in the first trimester) with acute flank pain (90 percent), which often radiates to the groin or lower abdomen. Hematuria is present in 75 to 95 percent, one-third of whom have gross hematuria, and approximately 40 percent will have pyuria [1,2]. These presenting symptoms are similar to those in nonpregnant patients. (See "Kidney stones in adults: Diagnosis and acute management of suspected nephrolithiasis", section on 'Symptomatic stones'.)

In a study of 27 pregnant patients who had a procedure to have their stones removed, the composition in 20 was predominantly calcium phosphate [9].

DIAGNOSIS IN PREGNANCY

Laboratory testing — All pregnant patients with suspected nephrolithiasis should undergo basic laboratory testing, similar to that performed in nonpregnant patients with suspected nephrolithiasis. This is discussed elsewhere. (See "Kidney stones in adults: Diagnosis and acute management of suspected nephrolithiasis", section on 'Laboratory testing'.)

Diagnostic imaging — Patients with suspected nephrolithiasis should undergo an imaging study to determine if a kidney stone is present and to assess for signs of urinary obstruction (eg, hydronephrosis). (See "Kidney stones in adults: Diagnosis and acute management of suspected nephrolithiasis", section on 'Diagnostic imaging'.)

The approach to the choice of diagnostic imaging is as follows:

●In pregnant patients suspected of having an obstructing stone, kidney/pelvic ultrasonography is the preferred initial imaging modality. This modality avoids exposure to radiation and is useful for detecting secondary signs of obstruction, such as hydronephrosis or hydroureter. However, physiological hydronephrosis of pregnancy (image 1) must be distinguished from pathological hydronephrosis from obstruction (image 2) (see "Maternal adaptations to pregnancy: Renal and urinary tract physiology"). For this distinction, it is helpful to image patients lying on their side with the symptomatic side up, thereby potentially moving the weight of the gravid uterus off the distal ureter. Rarely, pelvic or transvaginal ultrasound may identify a stone obstructing the distal ureter (image 3) [10,11].

The ability of ultrasonography and other imaging modalities to detect nephrolithiasis was retrospectively evaluated in a study of 57 pregnant patients with 73 admissions for symptomatic nephrolithiasis [2]. When performed as the initial examination, kidney ultrasonography detected calculi in 21 of 35 cases (60 percent sensitivity).

●If further diagnosis is required following kidney/pelvic ultrasonography, two additional options are available; they are listed in our order of preference:

•Magnetic resonance (MR) urography, which is not associated with radiation exposure (image 4). (See "Diagnostic imaging in pregnant and lactating patients", section on 'Magnetic resonance imaging'.)

•Low-dose computed tomography (CT) can be used in the second and third trimester but not the first trimester, when the fetus is most susceptible to radiation-induced injury. Some evidence suggests that low-dose CT is highly sensitive and specific for the detection of kidney and ureteral calculi in pregnant patients, and the radiation dose should confer a low risk of fetal harm [12,13]. (See "Diagnostic imaging in pregnant and lactating patients".)

Our recommendations are consistent with those made by the American Urological Association (AUA) technology assessment on imaging in the management of ureteral stone disease [14].

MANAGEMENT — Management of the pregnant patient with nephrolithiasis can be complex and frequently requires close collaboration among the patient, radiologist, obstetrician, and urologist.

Supportive care — Supportive care for pregnant patients presenting with acute renal colic includes pain control and, in selected patients, medical expulsive therapy to facilitate stone passage. (See "Kidney stones in adults: Diagnosis and acute management of suspected nephrolithiasis", section on 'Acute management'.)

Pain control — During an acute episode of renal colic, management is focused on pain control. If drugs are needed to relieve pain, acetaminophen is probably the safest choice but may not be sufficient. The use of nonsteroidal antiinflammatory drugs (NSAIDs) and opioids carry risks in pregnant patients and is discussed separately:

●NSAIDs – (See "Safety of rheumatic disease medication use during pregnancy and lactation", section on 'NSAIDs' and "Prenatal care: Patient education, health promotion, and safety of commonly used drugs", section on 'NSAIDs'.)

●Opioids – (See "Prenatal care: Patient education, health promotion, and safety of commonly used drugs", section on 'Opioids'.)

Stone passage — Most (75 to 85 percent) stones pass spontaneously due, in part, to the normally dilated urinary tract in pregnant patients [1,2]. (See "Maternal adaptations to pregnancy: Renal and urinary tract physiology".)

While the use of alpha blockers such as tamsulosin has been shown to facilitate ureteral stone passage in nonpregnant patients, the safety and efficacy of these agents in pregnant patients are less certain. We engage in shared decision-making regarding the use of alpha blockers for stone passage given the limited evidence supporting their safe use in this patient population. Limited data from retrospective studies have not shown any significant differences in maternal and infant outcomes between pregnant patients receiving or not receiving tamsulosin [15,16]. In one study of 207 pregnant patients with renal colic, the spontaneous stone passage rate was 58 percent among those receiving tamsulosin compared with 43 percent among those who did not receive tamsulosin, but this difference was not statistically significant [16]. (See "Kidney stones in adults: Diagnosis and acute management of suspected nephrolithiasis", section on 'Medical expulsive therapy'.)

Medical therapy for prevention of stone recurrence — Pregnant patients with established kidney stone disease may benefit from some of the same measures used to prevent recurrent stone formation in nonpregnant patients, such as increased fluid intake. However, the individual approach to medical preventive therapy depends upon a comprehensive evaluation of the patient's metabolic risk factors for stone formation, which we typically do not perform during pregnancy. Such an evaluation, and any preventive measures that would be initiated based upon the results of this evaluation, should be deferred until several months postpartum. (See "Kidney stones in adults: Prevention of recurrent kidney stones" and "Kidney stones in adults: Evaluation of the patient with established stone disease".)

Surgical management

Indications and timing of procedure — The indications for emergency and elective surgical stone management in pregnant patients are similar to those in nonpregnant patients and are discussed elsewhere. (See "Kidney stones in adults: Surgical management of kidney and ureteral stones", section on 'Indications and contraindications'.)

The timing of surgical stone management depends upon whether the patient has an emergency or elective indication for surgery and the severity of the patient's symptoms:

●In pregnant patients with an indication for emergency surgery (eg, obstructing stones and evidence of urinary tract infection [UTI], sepsis, or acute kidney injury [AKI]), urgent decompression of the collecting system should be performed without delay, regardless of the trimester. (See 'Emergency surgery' below.)

●In pregnant patients who do not require emergency surgery and have an indication for elective surgery, stone removal should ideally be delayed until after delivery. However, if the patient has intractable pain or recurrent UTI associated with a stone, surgical stone removal can be performed during pregnancy and is best performed during the second or third trimester. If intractable pain occurs in the first trimester, ureteral stenting or nephrostomy tube placement should be performed to relieve symptoms and stone removal should be deferred until the second or third trimester. In such patients, stent or nephrostomy tube exchange every four to six weeks is necessary due to a higher risk of stent/tube encrustation during pregnancy. (See "Nonobstetric surgery in pregnant patients: Patient counseling, surgical considerations, and obstetric management", section on 'Timing of surgery'.)

Choice of surgical approach

Emergency surgery — Patients with obstructing stones and either suspected or confirmed UTI or AKI require urgent decompression of the collecting system. (See "Kidney stones in adults: Surgical management of kidney and ureteral stones", section on 'Emergency surgery'.)

In pregnant patients who require urgent decompression of the collecting system, either ureteral stenting or placement of a nephrostomy tube is a valid option. However, pregnancy significantly increases the risk of stent encrustation, necessitating the need for frequent ureteral stent exchange every four to six weeks until delivery [17].

Elective surgery — Elective stone removal surgery may be appropriate for pregnant patients who fail to spontaneously pass the stone and who develop UTI, persistent urinary obstruction, or persistent, severe pain [18]. For pregnant patients with obstructing ureteral or kidney stones, we suggest ureteroscopy (URS) with laser lithotripsy as the surgical procedure of choice. Although shock wave lithotripsy (SWL) has been inadvertently performed in only a few pregnant patients [19,20], without complications, its use during pregnancy is contraindicated due to potential risks to the fetus. Similarly, percutaneous nephrolithotomy (PNL) for large volume kidney stones is contraindicated during pregnancy. In patients with large kidney stones that would normally be managed with PNL, temporary ureteral stenting or percutaneous nephrostomy tube placement to decompress the collecting system should be performed, and PNL should be deferred until after delivery. (See "Kidney stones in adults: Surgical management of kidney and ureteral stones", section on 'Choice of surgical approach'.)

With URS, small caliber ureteroscopes minimize or eliminate the need for concomitant fluoroscopic monitoring. If additional monitoring is needed, ultrasonography (no ionizing radiation) or pulsed fluoroscopy (minimal ionizing radiation) can be used. Another option to reduce radiation exposure to the fetus while performing URS is to use an inverted fluoroscope's C-arm [21].

URS appears to be similarly safe in pregnant and nonpregnant patients. A 2009 systematic review and meta-analysis of 14 reports noted nine complications with this technique among 108 pregnant patients [22]. These included two patients with postoperative pain managed by analgesia, five with UTIs, one with preterm uterine contractions treated by tocolytic, and one with a ureteral perforation managed by a stent. There were no life-threatening complications or deaths. The review also reported that the cases were from centers with operators that were highly skilled, a likely contributor to success with the technique. A similar rate of ureteral injury and UTI was reported in a multinational meta-analysis of URS in nonpregnant patients. (See "Kidney stones in adults: Surgical management of kidney and ureteral stones", section on 'Ureteroscopy'.)

Holmium laser lithotripsy is currently the preferred technique of stone fragmentation during URS as this device delivers energy to a localized area (depth of penetration is only 0.4 mm), can be used with flexible ureteroscopes, and is effective with stones of all compositions. The potential efficacy was illustrated in a report of eight pregnant patients with 10 symptomatic ureteral calculi and two encrusted ureteral stents who underwent URS and holmium:yttrium-aluminum-garnet (YAG) laser lithotripsy at a mean gestational age of 22 weeks; the mean stone size was 8.1 mm [23]. Procedural success was achieved in all but one case (91 percent), with no obstetric or urologic complications [24].

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Kidney stones".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Beyond the Basics topic (see "Patient education: Kidney stones in adults (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●General principles – The development of a symptomatic stone during pregnancy is a rare event, usually presenting in the second or third trimester with acute flank pain radiating to the groin or lower abdomen and hematuria. Normal pregnancy is associated with a mild increase in urine calcium excretion and a rise in urine pH; these are risk factors for calcium phosphate stones, which appear to be the most common kidney stone in pregnancy. Urinary stasis, due both to increased progesterone and a diminished fluid intake associated with reduced bladder capacity, may also contribute to stone formation. (See 'Epidemiology' above and 'Risk factors in pregnancy' above and 'Clinical presentation' above.)

●Diagnosis – All pregnant patients with suspected nephrolithiasis should undergo basic laboratory testing and a diagnostic imaging study, preferably with kidney/pelvic ultrasonography, to determine if a kidney stone is present and to assess for signs of urinary obstruction (eg, hydronephrosis). However, physiological hydronephrosis of pregnancy must be distinguished from pathological hydronephrosis from obstruction (image 2). If further diagnosis is required following kidney/pelvic ultrasonography, additional imaging options include magnetic resonance (MR) urography, which is not associated with radiation exposure (image 4), and low-dose computed tomography (CT), which can be used in the second and third trimester but not the first trimester. (See 'Laboratory testing' above and 'Diagnostic imaging' above.)

●Management – Management of the pregnant patient with nephrolithiasis can be complex and frequently requires close collaboration among the patient, radiologist, obstetrician, and urologist.

•Supportive care – During an acute episode of renal colic, management is focused on pain control. If drugs are needed to relieve pain, acetaminophen is probably the safest choice. Most (75 to 85 percent) stones pass spontaneously due, in part, to the normally dilated urinary tract in pregnant patients. While the use of alpha blockers such as tamsulosin has been shown to facilitate ureteral stone passage in nonpregnant patients, the safety and efficacy of these agents in pregnant patients are less certain. We engage in shared decision-making regarding the use of alpha blockers for stone passage given the limited evidence supporting their safe use in this patient population. (See 'Pain control' above and 'Stone passage' above.)

•Medical therapy to prevent stone recurrence – Pregnant patients with established kidney stone disease may benefit from some of the same measures used to prevent recurrent stone formation in nonpregnant patients, such as increased fluid intake. However, the individual approach to medical preventive therapy depends upon a comprehensive evaluation of the patient's metabolic risk factors for stone formation, which we typically do not perform during pregnancy. Such an evaluation, and any preventive measures that would be initiated based upon the results of this evaluation, should be deferred until several months postpartum. (See 'Medical therapy for prevention of stone recurrence' above.)

•Surgical management

-Indications – The indications for emergency or elective surgical stone management in pregnant patients are similar to those in nonpregnant patients. (See 'Indications and timing of procedure' above and "Kidney stones in adults: Surgical management of kidney and ureteral stones", section on 'Indications and contraindications'.)

-Timing – In pregnant patients with an indication for emergency surgery (eg, obstructing stones and evidence of urinary tract infection [UTI], sepsis, or acute kidney injury [AKI]), urgent decompression of the collecting system should be performed without delay, regardless of the trimester. In pregnant patients who do not require emergency surgery and have an indication for elective surgery, stone removal should ideally be delayed until after delivery. However, if the patient has intractable pain or recurrent UTI associated with a stone, surgical stone removal can be performed during pregnancy and is best performed during the second or third trimester. If intractable pain occurs in the first trimester, ureteral stenting or nephrostomy tube placement should be performed to relieve symptoms and stone removal should be deferred until the second or third trimester. (See 'Indications and timing of procedure' above.)

-Choice of surgical approach – Patients with obstructing stones and either suspected or confirmed UTI or AKI require urgent decompression of the collecting system with a ureteral stent or percutaneous nephrostomy tube. For pregnant patients undergoing elective stone removal surgery, we suggest ureteroscopy (URS) with laser lithotripsy; shock wave lithotripsy (SWL) and percutaneous nephrolithotomy (PNL) are contraindicated during pregnancy. (See 'Emergency surgery' above and 'Elective surgery' above and "Kidney stones in adults: Surgical management of kidney and ureteral stones", section on 'Choice of surgical approach'.)